The present invention relates to an operation monitor system capable of verifying the operation of solenoid operated devices such as solenoid valves and solenoid relays to which operation commands have been issued and continuously monitoring the operation of the solenoid operated devices when such solenoid operated devices are controlled, and more particularly to an operation monitor system which is suitable for use in combination with a remote control system for the solenoid operated devices.
In various plants, different valve means and relay means are used for various control purposes. The present invention is concerned with the solenoid operated devices of those means. The solenoid operated devices include the solenoid relays or solenoid valves, more particularly relays or valves which can assume binary states, that is, open state and close state and can switch the state by the action of electromagnet force. In the solenoid valve, a valve is normally at full open position or full close position by the action of spring force. When an exciting input is applied to an exciting coil, an electromagnet force is produced, which overcomes the spring force to move the valve to the full open position if it has been at the full close position, or to the full close position if it has been at the full open position.
In recently constructed plants, those solenoid operated devices are sometimes remotely controlled. In such cases, a central control room is located at a station remote from the installation room of the solenoid operated devices to centrally control the plurality of solenoid operated devices. In many cases, the distance from the installation room to the central control room is in the order of several hundreds meters. Accordingly, the remote control system employing a so-called data way system in which digital coded signals are transmitted and received to control the solenoid operated devices is used. This control system is suitable for use in a plant having an extensive plant area or a plant including a site located in an area which must be sealed.
One example of a plant which actually employs such a control system is a hydraulic control unit for control rods for adjusting the output of a boiling water type nuclear reactor electric power generating plant. The hydraulic control unit includes several solenoid valves per control rod, and the direction of the movement of the control rod is determined by opening or closing a particular one of the solenoid valves so that the power of the nuclear reactor is increased or decreased. By way of example, in a nuclear reactor electric power generating plant of the 1100 MWh class, the number of the control rods amounts to 200 and the number of solenoid valves amounts to 800. As the control rods are inserted into the nuclear reactor, the power of the nuclear reactor decreases and as the control rods are withdrawn the power of the nuclear reactor increases.
The following article introduces and outlines the control system of the hydraulic control unit of a nuclear reactor plant: "Multiplexed Rod Drive Control System for a General Electric BWR" by D. W. Reigel, E. E. Goodale and S. E. Moore, Conference Paper C 73 203-7, a paper recommended by the IEEE Power Generation Comittee of the IEEE Power Engineering Society for presentation at the IEEE PES Winter Meeting, New York, N.Y. Jan. 28-Feb. 2, 1973; manuscript submitted Sept. 14, 1972, made available for printing Dec. 11, 1972.
According to the above paper, in the remote control system employing a data way system, unique address codes are assigned to respective ones of the plurality of solenoid valves in the installation room. The central control room converts the address codes of the solenoid valves to be operated and the contents of the operations into digital coded signals and applies them as command words to the data way between the installation room and the central control room. The digital coded signals transmitted to the field over the data way are applied to actuation circuits provided one for each of the solenoid valves. Each of the actuation circuits decodes the address code of the transmitted digital coded signal, and when it coincides with the address assigned to its own solenoid valve, it controls the open/closed operation of its own solenoid valve in accordance with the content of operation transmitted. In the installation room, the operation status of the solenoid valve to which the command word was applied is converted into an acknowledge word, which is then sent back to the control room. The control room compares the acknowledge signal with the corresponding command word to check whether the solenoid valve has been operated properly. The command words include two signals, one being a control signal N used to actually drive the control rod and the other being a test signals S used to test the solenoid valve. In the following description, when it is not necessary to distinguish the signal N from the signal S, they are referred to as the command word. The command word consists of a synchronizing signal part, an address signal part to specify the solenoid valve or control rod, and an operation signal part to indicate the content of the operation. The acknowledge word which is derived encoding the operation status of the solenoid valve and sent back to the central control room is assembled each time the command word is applied, and transmitted. Accordingly, the acknowledge word is transmitted whether the command word is the signal N or the signal S. The format of the acknowledge word is basically similar to that of the command word with the exception that the operation signal part is replaced by an acknowledge signal section.
This system senses a voltage across the coil of the solenoid valve and edits the sensed information into the acknowledge word, which is then compared for verification. However, there is a problem here because the exciting power for the coil is an A.C. power. Namely, when a switch for exciting the coil is closed in response to the command word, the voltage across the coil is substantially zero, but since the voltage of the A.C. supply may be near zero potential it is not possible to discriminate whether zero potential occurs due to the closure of the switch or due to the zero potential of the A.C. supply voltage, by merely sensing the zero voltage across the coil. Thus, if the switch was not closed when the command word was applied but it happened that the A.C. supply voltage was small at that moment, the actuation circuit would be determined to be normal. Furthermore, it cannot always be determined that the solenoid valve has been operated from the fact that the switch has been closed because the valve might have been stuck in one position even though the coil has been excited.